Chapter 15, Problem 15.18P

Draw all constitutional isomers formed when each alkene is treated with $\text{NBS}+hv$.

a. b. c.

Interpretation Introduction

(a)

Interpretation: The constitutional isomer formed by the reaction of given alkene with $\text{NBS}+hv$ is to be drawn.

Concept introduction: The reaction of alkene with $N-\text{bromosuccinimide}$ in presence of light results in the formation of allylic halide. $\text{NBS}$ is the source of ${\text{Br}}_{\text{2}}$. Allylic halogenation results in the formation of two product mixture. Abstraction of hydrogen from allylic carbon result in the formation of a resonance stabilized radical. These two resonance structures react with ${\text{Br}}_{\text{2}}$ to form constitutional isomers as products.

Answer to Problem 15.18P

The constitutional isomers formed by the reaction of given alkene with $\text{NBS}+hv$ are,

Explanation of Solution

The reaction of alkene with $N-\text{bromosuccinimide}$ in presence of light results in the formation of allylic halide. $\text{NBS}$ is the source of ${\text{Br}}_{\text{2}}$. Allylic halogenation results in the formation of two product mixture. Abstraction of hydrogen from allylic carbon result in the formation of a resonance stabilized radical. These two resonance structures react with ${\text{Br}}_{\text{2}}$ to form constitutional isomers as products.

The given alkene is shown below.

Figure 1

The general steps involved in the reaction of allylic bromination with $\text{NBS}$ are stated below.

• The first step is the initiation of bromine radical.

• The next step is the propagation in which generation of allylic radical take place.

• In third step, allylic radical reacts with ${\text{Br}}_{\text{2}}$ to form allylic halide.

The constitutional isomer formed by the reaction of given alkene with $\text{NBS}+hv$ are shown below.

Figure 2

Therefore, the constitutional isomers formed for the given reaction are $1-\text{bromobut}-2-\text{ene}$ and $3-\text{bromobut}-1-\text{ene}$.

Conclusion

The constitutional isomers formed by the reaction of given alkene with $\text{NBS}+hv$ are shown in Figure 2.

Interpretation Introduction

(b)

Interpretation: The constitutional isomer formed by the reaction of given alkene with $\text{NBS}+hv$ is to be drawn.

Concept introduction: The reaction of alkene with $N-\text{bromosuccinimide}$ in presence of light results in the formation of allylic halide. $\text{NBS}$ is the source of ${\text{Br}}_{\text{2}}$. Allylic halogenation results in the formation of two product mixture. Abstraction of hydrogen from allylic carbon result in the formation of a resonance stabilized radical. These two resonance structures react with ${\text{Br}}_{\text{2}}$ to form constitutional isomers as products.

Answer to Problem 15.18P

The constitutional isomers formed by the reaction of given alkene with $\text{NBS}+hv$ are,

Explanation of Solution

The reaction of alkene with $N-\text{bromosuccinimide}$ in presence of light results in the formation of allylic halide. $\text{NBS}$ is the source of ${\text{Br}}_{\text{2}}$. Allylic halogenation results in the formation of two product mixture. Abstraction of hydrogen from allylic carbon result in the formation of a resonance stabilized radical. These two resonance structures react with ${\text{Br}}_{\text{2}}$ to form constitutional isomers as products.

The given alkene is shown below.

Figure 3

The general steps involved in the reaction of allylic bromination with $\text{NBS}$ are stated below.

• The first step is the initiation of bromine radical.

• The next step is the propagation in which generation of allylic radical take place.

• In third step, allylic radical reacts with ${\text{Br}}_{\text{2}}$ to form allylic halide.

The constitutional isomer formed by the reaction of given alkene with $\text{NBS}+hv$ are shown below.

Figure 4

Therefore, the constitutional isomers formed for the given reaction are $6-\text{bromo}-3,3-\mathrm{di}\text{methylcyclohex}-1-\text{ene}$ and $3-\text{bromo}-4,4-\mathrm{di}\text{methylcyclohex}-1-\text{ene}$.

Conclusion

The constitutional isomers formed by the reaction of given alkene with $\text{NBS}+hv$ are shown in Figure 4.

Interpretation Introduction

(c)

Interpretation: The constitutional isomer formed by the reaction of given alkene with $\text{NBS}+hv$ is to be drawn.

Concept introduction: The reaction of alkene with $N-\text{bromosuccinimide}$ in presence of light results in the formation of allylic halide. $\text{NBS}$ is the source of ${\text{Br}}_{\text{2}}$. Allylic halogenation results in the formation of two product mixture. Abstraction of hydrogen from allylic carbon result in the formation of a resonance stabilized radical. These two resonance structures react with ${\text{Br}}_{\text{2}}$ to form constitutional isomers as products.

Answer to Problem 15.18P

The constitutional isomers formed by the reaction of given alkene with $\text{NBS}+hv$ are,

Explanation of Solution

The reaction of alkene with $N-\text{bromosuccinimide}$ in presence of light results in the formation of allylic halide. $\text{NBS}$ is the source of ${\text{Br}}_{\text{2}}$. Allylic halogenation results in the formation of two product mixture. Abstraction of hydrogen from allylic carbon result in the formation of a resonance stabilized radical. These two resonance structures react with ${\text{Br}}_{\text{2}}$ to form constitutional isomers as products.

The given alkene is shown below.

Figure 5

The general steps involved in the reaction of allylic bromination with $\text{NBS}$ are stated below.

• The first step is the initiation of bromine radical.

• The next step is the propagation in which generation of allylic radical take place.

• In third step, allylic radical reacts with ${\text{Br}}_{\text{2}}$ to form allylic halide.

The constitutional isomer formed by the reaction of given alkene with $\text{NBS}+hv$ are shown below.

Figure 6

Therefore, the constitutional isomers formed for the given reaction are $3-\text{bromo}-2-\text{ethylbut}-1-\text{ene}$ and $3-\left(\text{bromoethyl}\right)\text{pent}-2-\text{ene}$.

Conclusion

The constitutional isomers formed by the reaction of given alkene with $\text{NBS}+hv$ are shown in Figure 6.